Plato seeks to explain the difference between clear intellectual vision and the confused vision of sense perception by an analogy from the sense of sight. Sight, he says, differs from the other senses, since it requires not only the eye and the object, but also light. The eye is compared to the soul, and the sun, as the source of light, to truth or goodness. The soul when turned towards the twilight of becoming and perishing has opinion only first of one opinion, then of another, and seems to have no intelligence what imparts truth to the known and the power of knowing to the knower is what I would have you term the idea of the goodp. 124.

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